A conventional infrared ray lamp causes a problem wherein its power consumption increases abnormally after use for a long time, and its heating portions fuse and break in some cases. This problem will be described below.
As an infrared ray lamp conventionally used as a heat source, an infrared ray lamp having a tungsten spiral filament held at the central portion of a glass tube by a number of supports of tungsten is used. However, the infrared ray emission rate of the tungsten is so low as, 30 to 39%, and the rush current at the time of turning on is high. Furthermore, it is necessary to use a number of the tungsten supports for holding the tungsten spiral filament at the central portion of the glass tube, and the assembly work for them was not easy. In particular, sealing the plural tungsten spiral filaments in the glass tube in order to obtain high output was very difficult.
In order to solve these problems, an infrared ray lamp, wherein a carbon-based substance formed into a rod shape is used instead of the tungsten spiral filaments as a heating element, has been proposed conventionally. As such a conventional infrared ray lamp, an infrared ray lamp disclosed in Japanese Published Unexamined Patent Application, Publication No. Hei 11-54092 applied by the same applicant as that of the present invention is available. Since the carbon-based substance has a high infrared ray emission rate of 78 to 84%, the infrared ray emission rate of the infrared ray lamp also becomes high by using the carbon-based substance as a heating element. Furthermore, since the carbon-based substance has a negative resistance temperature characteristic wherein its resistance value lowers as the temperature rises, the carbon-based substance has a significant characteristic of capable of reducing its rush current at the time of turning on.
FIGS. 20 and 21 are front views showing the conventional infrared ray lamp described in Japanese Published Unexamined Patent Application, Publication No. Hei 11-54092, wherein the carbon-based substance is used as a heating element. Part (a) of FIG. 20 is a view showing the structure of the lead wire taking-out portion of the conventional infrared ray lamp in which a heating element 200 is sealed inside a glass tube 100. Part (b) of FIG. 20 is a partially magnified view showing the connection portion between the heating element 200 and the lead wire 104 of the infrared ray lamp shown in the part (a) of FIG. 20. FIG. 21 is a partially magnified view showing the connection portion between the two heating elements 200a and 200b and the lead wire 104 of the conventional infrared ray lamp in which the two heating elements 200a and 200b are sealed inside the glass tube. The part (a) of FIG. 20 shows the structure of one end of the infrared ray lamp, and the other end of the infrared ray lamp has similar structure. Furthermore, the structure of the infrared ray lamp shown in FIG. 21 is similar to that shown in the part (a) of FIG. 20, except for the connection portion between the two heating elements 200a and 200b and the lead wire 104 shown in the figure.
As shown in the part (a) of FIG. 20, in the conventional infrared ray lamp, a metal wire 102 wound in a coil shape is wound around the end of the heating element 200 formed of a carbon-based substance and formed into a rod shape. The end portion of the coil-shaped metal wire 102 is covered with a metal foil sleeve 103, and this metal foil sleeve 103 is secured to the end of the heating element 200 by crimping. The internal lead wire 104 formed of a metal wire and having a coil portion 105 wound in a coil-spring shape in the middle of the wire is electrically bonded to one end of the metal foil sleeve 103. One end of a molybdenum foil sheet 107 is spot-welded to the other end of the internal lead wire 104. Furthermore, an external lead wire 108 formed of a molybdenum wire is welded to the other end of the molybdenum foil sheet 107. The heating element 200, the metal foil sleeve 103, the internal lead wire 104, the molybdenum foil sheet 107 and the external lead wire 108 connected in series as described above are inserted into the glass tube 100 and disposed therein. An inert gas, such as argon, nitrogen or the like, is sealed inside the glass tube 100, the glass tube 100 is fused and bonded at the portion of the molybdenum foil sheet 107, thereby completing an infrared ray lamp.
FIG. 21 is a perspective view showing the inside of another conventional infrared ray lamp and showing the structure of the connection portion between the two heating elements 200a and 200b and the metal lead wire 104 of the conventional infrared ray lamp. As shown in FIG. 21, this conventional infrared ray lamp has a structure wherein the two heating elements 200a and 200b are sealed in one glass tube (not shown). In the infrared ray lamp shown in FIG. 21, coil-shaped metal wires 102a and 102b are wound around the end portions of the heating element 200a and 200b respectively, and metal foil sleeves 106 are fitted over the wires. The fitted metal foil sleeves 106 are secured to the end portions of the heating elements 200a and 200b by crimping. The metal lead wire 104 having a coil portion 105 wound in a coil-spring shape in the middle of the wire is electrically connected to the metal foil sleeves 106.
The infrared ray lamps having the above-mentioned structures have good infrared ray emission rates, since their heating elements are formed of a carbon-based substance; but, there are the following problems.
In the conventional infrared ray lamp having the structure shown in FIG. 20, for the lamp of large wattage of the infrared ray lamp, that is, for the lamp of a large power consumption, the coil-shaped metal wire 102 is heated to a high temperature. As a result, when the infrared ray lamp having this structure is used for a long time, the contact resistance of the connection portion among the heating element 200, the coil-shaped metal wire 102 and the metal foil sleeve 103 increases because of the temperature rise. The conventional infrared ray lamp therefore has the problem of abnormal heating at the connection portion. Furthermore, if the temperature at the connection portion between the coil-shaped metal wire 102 and the metal foil sleeve 103 rises continuously for a long time, the temperature at the bonding portion may rise high and, in the worst case, the bonding portion may fuse and break. Moreover, the stress caused by heat cycles due to the difference in thermal expansion coefficient between the heating element 200 and the coil-shaped metal wire 102 is added, and the contact resistance becomes higher than the value at the beginning of use, whereby the temperature rise at the connection portion is accelerated.
In addition, in the structure of the infrared ray lamp having the two heating elements 200a and 200b shown in FIG. 21, the following problems are caused.
In the process wherein both ends of the two heating elements 200a and 200b are crimped by using the metal foil sleeve 106, no problem occurs if the two heating elements 200a and 200b are crimped by a uniform tension or compression force; however, crimping may occur in a state of an unbalanced tension or compression force. In the conventional infrared ray lamp undergone crimping in such away, if the heating elements 200a and 200b are heated, the two heating elements 200a and 200b expand thermally in different states. For this reason, the imbalance of the tension or compression force applied to the heating elements 200a and 200b increases. In the case when the balance in the crimped state is improper in particular, one of the carbon-based heating elements, to which the larger tension or compression force is applied, may break.
Next, the problem of directivity in the conventional infrared ray lamp will be described below.
The infrared ray lamp is used as a heater for heating objects or for a space heater for heating rooms by using radiant infrared rays. As this kind of the conventional infrared ray lamp, an infrared ray lamp having the structure shown in FIG. 22 is known. FIG. 22 is a plan view showing an example of the conventional infrared ray lamp. FIG. 23 is a perspective view showing the infrared ray lamp shown in FIG. 22. In FIGS. 22 and 23, the central portion of the infrared ray lamp can be understood easily from the descriptions on both side portions shown in the figures, therefore, the central portion of the infrared ray lamp is not shown in either of the figures.
The conventional infrared ray lamp shown in FIGS. 22 and 23 comprises a substantially cylindrical glass tube 201, metal foil sheets 205 embedded in both end portions of the glass tube 201, a heating element 240 hermetically sealed inside the glass tube 201 and internal lead wires 204. The heating element 240 is a resistance wire formed of nichrome or tungsten and wound in a coil shape. The internal lead wires 204 are used to connect both ends of the heating element 240 to the metal foil sheets 205. As a result, the heating element 240 is electrically connected to the metal foil sheets 205 and pulled properly by the internal lead wires 204 on both sides, thereby secured stably. At this time, the center axis of the coil-shaped heating element 240 is disposed so as to be substantially coaxial with the center axis of the cylindrical glass tube 201.
As shown in FIGS. 22 and 23, the external lead wires 206 are connected to the metal foil sheets 205 on both sides respectively. When a voltage is applied across the external lead wires 206 taken out from both sides, a current flows through the heating element 240, and heat generates from the heating element 240 owing to the resistance of the heating element 240 corresponding to the current. At this time, infrared rays are emitted from the heating element 240.
Part (a) of FIG. 24 is a graph of the distribution curve 270 of the intensity of the infrared rays emitted from the heating element 240 of the infrared ray lamp shown in FIG. 23. Part (b) of FIG. 24 is a cross-sectional view showing the portion having the heating element 240 of the infrared ray lamp shown in FIG. 23. The x and y axes shown in the parts (a) and (b) of FIG. 24 are orthogonal coordinate axes on a plane perpendicular to the axial direction of the heating element 240 shown in FIG. 23. In the parts (a) and (b) of FIG. 24, the origin 0 corresponds to the center axis of the heating element 240. In the graph of the part (a) of FIG. 24, the values in the radial directions designate the emission intensity of the infrared rays, and the values in the circumferential directions designate angles with respect to the center axis on the plane perpendicular to the axial direction of the heating element 240. These angles are designated by angles from the positive direction of the x axis.
When a constant voltage was applied to the heating element 240, the amount of the infrared rays reaching a minute area at a constant distance from the center axis (represented by the origin 0 of FIG. 24) of the heating element 240 was measured, whereby the intensity distribution curve 270 was obtained.
As indicated by the intensity distribution curve 270 in the part (a) of FIG. 24, the infrared ray lamp 240 emits infrared rays in all directions at substantially similar intensity. This results from the fact that the cross-sectional shape of the heating element 240 is substantially symmetrical with respect to its axis and has a circular shape as shown in the part (b) of FIG. 24.
By the equally distributed infrared rays emitted in all directions at substantially similar intensity as described above, heat is transmitted from the heating element 240 to the outside and used to heat the outside and the surroundings.
In the conventional infrared ray lamp structured as described above, in the case when it is desired to give directivity to the emission intensity of the infrared rays, a structure is known wherein an infrared ray reflection plate is installed outside the infrared ray lamp for example.
FIG. 25 is a perspective view showing an example wherein an infrared ray reflection plate 280 is provided for the conventional infrared ray lamp and showing the positional relationship between the infrared ray lamp and the infrared ray reflection plate 280. The infrared ray reflection plate 280 has a semi-cylindrical shape and is disposed coaxially with the heating element 240 so as to surround the half of the heating element 240.
Part (a) of FIG. 26 is a graph of the distribution curve 271 of the intensity of the infrared rays emitted from the infrared ray lamp having the infrared ray reflection plate 280. Part (b) of FIG. 26 is a cross-sectional view showing the portion having the heating element 240 of the infrared ray lamp having the infrared ray reflection plate 280 shown in FIG. 25. The x and y axes shown in the parts (a) and (b) of FIG. 26 are orthogonal coordinate axes on a plane perpendicular to the axial direction of the heating element 240 shown in FIG. 25. The direction opposed to the reflection face of the infrared ray reflection plate 280 is defined as the negative direction of the x axis. In the parts (a) and (b) of FIG. 26, the origin 0 corresponds to the center axis of the heating element 240. In the graph of the part (a) of FIG. 26, the values in the radial directions represented the emission intensity of the infrared rays, and the values in the circumferential directions represented angles with respect to the center axis on the plane perpendicular to the axial direction of the heating element 240. These angles are designated by angles from the positive direction of the x axis. In the part (a) of FIG. 26, the concentric gradations indicating the emission intensity have the same values of the gradations shown in the part (a) of the above-mentioned FIG. 24. In addition, the method of measuring the emission intensity is the same as that in the case shown in the part (a) of FIG. 24.
As shown in the part (a) of FIG. 26, by providing the infrared ray reflection plate 280, infrared rays are emitted intensely only on one side of the infrared ray lamp, with the positive direction of the x axis used as the center.
As described above, in the conventional infrared ray lamp, it is indicated that the emission of the infrared rays has isotropic intensity distribution in all directions. For this reason, in order to give directivity to infrared ray emission, it is necessary to provide the infrared ray reflection plate outside the infrared ray lamp.
However, the infrared ray reflectivity of the infrared ray reflection plate is apt to be lowered because of aging and the adhesion of stains. As a result, the intensity distribution of the infrared ray emission becomes different with the direction of the emission. Furthermore, as the infrared ray reflectivity lowers, the amount of the infrared rays absorbed by the reflection plate itself increases. If this kind of heating apparatus is used for a long time, emission efficiency lowers, and unexpected parts will be overheated.
Furthermore, the emission intensity distribution obtained by providing the semi-cylindrical infrared ray reflection plate for the infrared ray lamp having the above-mentioned isotropic emission intensity distributions in all directions is substantially the same in a wide range on one side in general as shown in the part (a) of FIG. 26. For this reason, in the conventional infrared ray lamp, an attempt to increase the emission intensity in a more limited range and to decrease the intensity in other ranges in order to enhance directivity is difficult. As a result, in the case when the conventional heating apparatus is used for localized heating, the problem of low heating efficiency occurs.